MyLang

Grammar Definition

var is a Variable
num is a Number
type ::= `int` | `bool`
vardec ::= `(` `vardec` type var expression `)`
expression ::= num | `true` | `false` | var |
               `(` op expression expression `)`
loop ::= `(` `while` expression statement `)`
assign ::= `(` `=` var expression `)`
print ::= `(` `print` expression `)`
progn ::= `(` `progn` statement* `)`
statement ::= vardec | loop | assign | print | progn
op ::= `+` | `-` | `&&` | `||` | `<`
program ::= statement

Object language (our language): MyLang Metalanguage (what we are writing the compiler in): Java Target language (what we are compiling to): JavaScript

Tokens

Possible Tokens:

• IdentifierToken(String)
• NumberToken(int)
• IntToken: 0
• BoolToken: 1
• LeftParenToken: 2
• VardecToken: 3
• RightParenToken: 4
• TrueToken: 5
• FalseToken: 6
• WhileToken: 7
• SingleEqualsToken: 8
• PlusToken: 9
• MinusToken: 10
• LogicalAndToken: 11
• LogicalOrToken: 12
• LessThanToken: 13
• PrintToken: 14
• PrognToken: 15

AST Definition

interface Type

• class IntType: 0
• class BoolType: 1

interface Stmt

• class VardecStmt
• class WhileStmt
• class AssignStmt
• class PrintStmt
• class PrognStmt

interface Exp

• class NumberLiteralExp
• class BooleanLiteralExp
• class VariableExp
• class BinaryOperatorExp

interface Op

• class PlusOp: 2
• class MinusOp: 3
• class LogicalAndOp: 4
• class LogicalOrOp: 5
• class LessThanOp: 6

class Program

Types

• Vardec puts a variable in scope with a type
  • Need to remember the variable and the type
  • Need to ensure the expression is of the type
• num should be an int
• true and false should be bools
• var is whatever the type of the variable is
• while's expression is a boolean
• assign:
  • var should be in scope
  • var's type should match expression's type
• exp1 + exp2 => int, exp1: int, exp2: int
• exp1 - exp2 => int, exp1: int, exp2: int
• exp1 && exp2 => bool, exp1: bool, exp2: bool
• exp1 || exp2 => bool, exp1: bool, exp2: bool
• exp1 < exp => bool, exp1: int, exp2: int
• program: all statements are well-typed

Running the Code

mvn exec:java -Dexec.mainClass="mylang.MyLang" -Dexec.args="input_program.mylang output_program.js"